Monitoring cameras also referred to as surveillance cameras are frequently used to observe objects and activities in a scene. Information about what type of objects, the status of the objects and whether there are people or animals in the scene may, for example, be gathered. The monitoring cameras are advantageously digital network cameras allowing a remote observer to view image data captured by the camera and transferred via a network. To provide useful information to the observer, it is crucial that the camera is correctly directed such that objects of interests are within the field of view of the camera and the objects are in focus.
Pan-Tilt, PT, cameras allow, in contrast to stationary cameras where the field of view is set at the installation, for a movable field of view. Different regions of a scene may thereby be monitored. PT camera allows for an object to be followed and motion tracking techniques may further be provided allowing an object to be followed automatically even if it moves out from the field of view. Pant-Tilt-Zoom, PTZ, cameras offers improved performance as an adjustable zoom level allows for a transition from a long shot to a close-up viewing of an object or vice versa. Object of interest within a scene may thereby be viewed in greater detail.
Monitoring cameras using autofocusing methods simplifies the handling of the camera as ideally the camera will capture a clear image independent on if the field of view is changed by a tilt motion, pan motion and/or by zooming. It is, however, challenging to efficiently find focus as the field of view is changed, especially for scenes with low light or low contrast, that contains a lot of noise or where there are dramatic changes in light. To this end, rapid movements or other changes to the scene may result in lost focus and refocusing is needed to recover a clear image of the scene or objects within the scene. There is therefore a risk of information being lost as it may take some time for the camera to find focus. The observer may further feel discomfort as the focus appears to be coming and going repeatedly.
Thus, there is a need for more efficient focusing methods to focus a monitoring camera, in particular for PTZ cameras where the field of view is changed repeatedly.